The dyes of the present invention have both a sulfonic acid group and an azo group directly bonded to the same aromatic ring system and diaryl guanidine complexed to the sulfate. In many widely used dyes of this type, there are two such aromatic ring systems to which an azo and aryl guanadine-complexed sulfonic acid group are directly bonded. Dyes of this type are especially useful in inks, such as those used in ballpoint pens.
Dyes of this type are generally prepared by synthesizing compounds containing one or more aromatic ring systems directly to sulfonic acid and azo groups in an aqueous medium and then complexing this compound with a diaryl guanadine within the aqueous medium. The complexed dye precipitates from the aqueous medium as a fine powder which is collected, pressed and dried as a filter cake. In preparing inks from such dyes, the dyes are dissolved in an organic solvent system.
It has been found to be inconvenient and expensive to prepare solid complexed dyes and then to dissolve them in organic solvents. Handling powder is difficult and results in potentially hazardous human exposure. Powdered dyes are difficult to solubilize in organic solvents and invariably result in high insoluble levels. Also, it is difficult to produce dye solutions with high solids content by dissolving powdered complex dyes.
It is a general object of the present invention to produce liquid dyestuffs of the type in which a sulfonated aryl azo moiety is complexed with a diaryl guanidine without first producing a dye powder.